Method of forming layers for electronic cathodes



G. K. TEAL 91,

LAYERS FOR ELECTRONIC CATHODES Dec. 13, 1945.

METHOD/ OF FORMING Filed Nov. 26, 1942 1 muouzrsn BULBS FOR COLLECTING 36H;

REAG TION VESSEL INVENTOR GK TEAL ATTORNEY Patented Dec. 18, 1945 'METHOD OF-FORMING IEAYER'S FOR 1 ELECTRONIC CATHODES Gordon K. 'Teal, Summit, N. J., assignor to Bell- Telephone Laboratories, Incorporated, New York", N. Y., a corporation-ofNew York Application November 26, 1942, Serial No. 467,039

\ 18Claims.

This invention relates to methods of ,producing .layers for electronic cathodes-and more particularly to the. method comprising introducing a gaseous metallic hydride in contact. with a cathodecarrier to.b'e coated. and decomposing the hydride to form a layer of the metalon the carrier.

An object of the invention is to provide an improved method of making electronic cathodes.

.In anexampleof practice of theinvention a photoelectric cathode. is produced by introducing antimony hybride into a container within "which acathode carrierissupported, suchas a silver. plate provided with-a matrix including cesium oxide and adsorbed cesium. This matrix isheated and the antimony hydridein contact therewith is decomposed to produce a layer of antimony on the. matrix. The decomposing temperature'isabout 150 to 200 C.

(centig-rade). By controlling both thetimeof heating and the -area which is heated, the amount of. antimonydeposited may be accurately controlled. Thelayer. of antimony is in intimate contact withthe adsorbed cesium.

Theantimon maybe deposited. also. directly onglassor on a-semitransparent layer of silver, copper or other metal which has been deposited on glassor other carrier. The antimony may also be deposited onmetal plates or electrodes.

Cesium is depositedon the antimony in intimate contact therewith. Instead of antimony other metals may also be deposited from the gaseous state, such as the volatile hydrides. of the elements of the fourth and fifth groups of the periodic table, including among others, bismuth, arsenic, phosphorus, germanium and silicon.

The invention will now be described more in detail having reference to the accompanying drawing:

Fig; 1 hows a photoelectric tube,- partly in section, made according to this invention;

Fig; 2 is a fragmentary showing of aportion of the photoelectric tub'eof Fig. 1 to illustrate the structure of the cathode;

Fig. 3 is a camera tube, partly in section, having'a photoelectric cathode made according to thisinventi'on: r

Fig. 4 is a fragmentary showing of a portion of the tube of Fig. 3 to illustrate the structure of the photoelectric cathodeyand.

Fig. 5 illustrates schematically. apparatus used in the practice of thisinvention.

The same reference characters are. used to indicate identical-elements -.in1the several figures.

The photoelectricytubeof Fig. 1 is one form' of device which may be made by the method-of this invention. It comprises a glass bulb 5., partly in cross section, having a reentrant stem 6=throughwhich cathode lead-in conductor 1 and anode lead-in-conductor 8 are sealed and to which exhaust tubulation 9 is connected. The

andoe H1 in the form of a nickel ring is mounted on the lead-in conductor 8. The cathode is sup ported on the inner surface of the'bulb 5 and in contact with the inner end I I of lead-in conductor 1. A portion l2 of the bulb 5 is kept clear for the entrance of the energizing light beam.

The nature of the cathode is shown more clearly inFig. 2. On the inner surface of thebulb 5 a layer l3 of silver or other suitable metal is formed by vaporization and deposition or other suitable process. The surface of the silver layer I3 is then oxidized to forma-layer of silver oxide M. A thin layer. l5 of cesium is then deposited onthe layer of silver oxide and the evacuated tube is baked to produce maximum photosensitivity. After this baking process the layers l4 and h'r are probably no longer discrete but form a-composite matrix on the silver layer I3, which matrix, it is believed, comprises finely divided silver oxide, cesium oxide, pure silver and cesium. A layer N5 ofantimony is then formed on this matrix by introducing antimony hydride, SbH3, into the evacuated bulb5 andiheating the matrix to a temperature of to'200 C. to decompose the antimony-hydride. The efiect. of' this treatment is to improve the spectral sensitivity to wave-lengths in the blue regionof the spectrum.

The thickness of the layers l3, l4, l5 and I6, as shown in Fig. 2, is greatly exaggerated for purposes of illustration. In. an actual photoelectric tubemade according to this invention the silver layer l3 might be even semitransparent whilethe layers [4, I 5 and I6 wouldbe still thinner.

Another device which may conveniently be made by the method of this inventionis a socalled camera tube, as illustrated in Fig. 3. It comprises a spherical portion 20, an image portion .2| and an electron gun portion. 22, all made of glass. The spherical portion. 20 is provided with a reentrant stem 23 having a glass bracket supported therefrom, which bracket supports a mosaic target 25. Target 25 comprises a sheet of mica 26 on which a signal plate 21 is formed by the'depositionof evaporated aluminum. The oppositeface of. the sheet 26 is coated withsilver whichlis heat treated, oxidized and treated'with cesium to form a secondary electron emitting mosaic 28. Sealed through the stem 23 is a lead-in conductor 29 which is conductively connected to the signal plate 21. The image portion 2| is a cylindrical glass tube having a glass end portion 30. The inner surface of the tube 2| is provided with a plurality of conducting ring lectrodes 3| and a self-supporting metallic ring electrode 32. Electrode 32 serves as a support for a plurality of evaporator cups 33 used to evaporate a semitransparent layer of silver on the inner surface of the end portion 30 which is sensitized to form a photoelectric cathode. A lead-in wire 34 contacts the silver layer on the end 30. Lead-in wires 35 contact the electrodes 3|, respectively, and lead-in wire 36 contacts the electrode 32. The electron gun portion 22 comprises an electron beam producing electrode structure 31. It might also comprise beam deflecting plates.

The nature of the cathode structure on end portion 30 is shown more in detail in Fig. 4. On the semitransparent layer 38 of silver a layer 39 of antimony is formed according to the method of this invention. On the layer 39 a layer 40 of cesium is deposited. This cathode is photoelectrically sensitive so that when an optical image is projected on the photoelectric cathode through the glass end portion 30 a corresponding photoelectron image is formed which may be projected on the mosaic target 25 by the electron focusing electrodes 3| and 32 and a deposited electrode 42' of relatively large extent to which lead-in wire 43 is connected. Electrode 42 covers-a considerable portion of the left-hand side of spherical portion and extends into the image portion 2| and the cathode gun portion 22.

The process of sensitizing the camera tube of Fig. 3 is briefiy as follows:

The tube is first evacuated and baked at 400 C. to eliminate occluded gases. The evaporators 33 are heated to evaporate the silver which deposits in a semitransparent layer on the end portion 30 in contact with lead-in wire 34. The tube is kept cold as a whole while the end portion 30 is heated to a temperature of 100 to 200 C. by means of a hot-air blast. Antimony hydride gas is admitted through the pump tubulation 4| and is decomposed at the heated portion 30 to deposit antimony on the semitransparant silver layer. 38. After a suitable amount of antimony has been deposited the remaining antimony hydride gas is pumped out of the tube and pump station. Oxygen is now introduced into the tube and the mosaic of silver 28 is oxidized by electrodeless discharge. The oxygen is pumped out and cesium is introduced by chemical reaction of a cesium producing pellet. The pellet or pellets, if it is convenient to use more than one pellet, may be mounted within the tube or in a side tube connected to the main tube. After the cesium has been flashed the tube is heated to 150 to 200 C. to distribute the cesium to the oxidized mosaic 28 and to the antimony layer 39 on the end portion 33. The tube is baked and tested alternately until maximum sensitivity is obtained. Any excess of cesium may be taken up by a square of tin oxide painted on the exposed surface of the signal plate 21.

In a modified method of sensitization the an-' timony layer may be formed on the silver layer 38 by an electrical discharge in the antimony hydride in the vicinity of the silver layer 38, the antimony hydride being decomposed by the discharge. In another modified method of sensitization the semitransparent layer of silver 38 may first be partially oxidized and then exposed to antimony hydride while. heated to a temperature of 150 to 200 C. The antimony hydride reacts with the silver oxide and produces SbaA or Ag and SbzOzs or silver antimonate. Treatment of these surfaces with cesium produces a sensitive photoelectric cathode.

A method of making antimony hydride gas will now be described having reference to Fig. 5. The antimony hydride is formed by chemical reaction in a reaction vessel 45. The gas passes through tube 46 into a carbon dioxide trap 41 used to condense out water vapor. The antimony hydride then passes through a tube including stop cock 48 into a liquid nitrogen trap 49 wherein the antimony hydride is trapped by being solidified during the reaction process. Excess hydrogen produced by the reactionis freed by opening the stop cock 40. During the reaction process the stop cock 5| is closed. The antimony hydride from trap 49 may be collected in gaseous form in bulbs 52 which are first evacuated through pump tubulation 53. The pressure in the bulbs 52 is indicated by a manometer 54. The stop cock 55 controls the bulbs 52 and stop cock 56 controls the connection to the pump tubulation 53.

A suitable reaction for producing antimony hydride results from treating an alloy of antimony and zinc with dilute sulphuric acid, H2804, in the reaction vessel 45. At the start of the reaction the vessel 45 is cooled in an ice bath to control the speed of the reaction. The alloy may be prepared by fusing pieces of antimony and zinc in the proportions by weight of 9 grams of antimony to 28 grams of zinc. The antimony and zinc in'the form of sticks are broken into pieces about one-quarter inch in length and placed in a porcelain crucible which is covered with another smaller crucible. This combina tion is heated from below by a Meker burner and from above with a sealing-off torch and a soft flame. The heating requires approximately forty-five minutes, toward the end of which the crucible begins to bump as though the mixture were boiling or reacting violently. After cooling the resulting ingot of alloy is removed from the crucible and crushed with a hammer on a steel plate into pieces about the size of peas. The crushed alloy is @placed in the reaction vessel 45, together .with about 50 cubic centimeters of water. Dilute sulphuric acid, prepared by mixing 25 cubic centimeters of concentrated H2804 with cubic centimeters of water, is added to the alloy through the stoppered funnel 51 in 25 cubic centimeter portions during the course of about five hours, keeping the reaction vessel immersed in an ice bath. During this reaction the stop cock 5| is kept closed and the stop cook 48 open. Water vapor is collected. in the carbon dioxide trap 41 and solid antimony hydride in the liquid nitrogen trap 49. The stop cock 48 is then closed and stop cock 5| opened. The equipment on the right-hand side of stop cook 48 is thoroughly evacuated. The stop cock 56 is then closed to cut ofi the pump tubulation 53. As the liquid nitrogen trap 49 is allowed to warm up the liquid antimony hydride evaporates and is collected in any one or all of the bulbs 52 under control of the stop cock 55. After the antimony hydride has been collected the stop cock 5| is closed and the antimony hydride in bulbs 52 is ready for use in making devices such as are Q StOpxCOCkS in the: pump tubulation (11015 1 smash:

allof thebulbs 52} g I Another. react-ion -forproducing antimonyhyj flf'hesmethod on'formingia layer!!! antimony whichz comrises l depositineva layenof': silver onthe inside aoffanaemcuatediglassbulb, :andmeating.

the; la' tyer-s ofrsilreruimthe nesenceiof? antimony;

dride results from treating an' alloy of I and zinc "withdilute hydrochloricacid; HG-l; crushed alloy is placedin 1 the reaction-vessel and the entire system is flushedT'wi-th tank-hydro; gen. Dilute HCl is then dropped on-thealloy by means of the stoppered funnel 5T, keeping-- the vessellli surrounded wi tlr an ice bath. Thedilute HCl consists of one volumeof concentrated HGI mixedwithzaboutthree yolumesof-waterq About 50' cubic centimeters of the dilute H01 5 are added immediately. The reaction-takes place atareasonable rate of about: one to .a three bubhles per second. The reaction. may continue for several hours. The antimony hydride which iscollectedin the liquid nitrogen trap may be used in-the sameimanner as hereinbefore described.

Still another reaction for producing antimony hydride comprises dropping a solution of 10 grams of antimony chloride, SbCls in concentrated hydrochloric acid, HCl, diluted with an equal volume of water onto granulated zinc and dilute HCl in the reaction vessel 45. The dilute HCl is allowed to react with the zinc for about fifteen minutes to sweep the air out of the system through the outlet tube 50. The antimony chloride solution is then allowed to drop in slowly, the reaction taking place at atmospheric pressure. Here again the antimony hydride is collected as a solid in the liquid nitrogen trap 49. It may be used in the manner hereinbefore described.

What is claimed is:

l. The method of making a light-sensitive cathode which comprises forming on a cathode 'carrier a deposit of antimony and cesium in intitainer, decomposing said gas, and forming on said cathode carrier a deposit of the antimony resulting from the decomposition.

2. The method of making a light-sensitive cathode which comprises depositing cesium on oxidized silver, heat treating said cesium, silver and silver oxide to form a matrix which is sensitive to light, and further heating said matrix in the presence of antimony hydride gas to a temperature sufficient to decompose said antimony hydride to form a deposit of antimony on said matrix.

3. The method of making a light-sensitive cathode which comprises depositing a silver layer on the inside of an evacuated glass bulb, oxidizing the surface of said silver layer, exposing said oxidized surface to cesium vapor, heating the bulb to cause some of said cesium to react with someof said silver oxide, introducing antimony hydride into the bulb, and heating the bulb to. a temperature which decomposes the antimony hydride.

4. The method of making a light-sensitive v cathode which comprises depositing a silver layer on the inside of an evacuated glass bulb, oxidizing the surface of said silver layer, exposing said oxidized surface to cesium vapor, heating the bulb to cause some of said cesium to react with some hydride-do decompose the .antimonyhydrid'euand' depesit:-a.::1ayer:ofrantimonyronzsaidr silver layer.

, 5; Erie method mf'eforming a layerof antimonywhioh omnprises denositingmlayenof'silver onxthe inside a evacnatedglassw bulb,- .heatmg the layer of silyer in the-prmencepfiantimonyhydride to decompose the antimony hydride and'depositz a; layersofi antimorryr omsaid silverlayer,. and depositing a layercf onsaidalayer: of an.

'i'rThemethodiiof making a: lightesensitive thodes which-comprises: depositing alayer of: silver; onwa portionrof; the :inside .surf-acevof' an evacuatedifglassr-tube;oxidizing the surface of said. silyerr layen; exposingsaidoxidized? silver: layer to antimony hydride gas, and heatingsaid. layer:totdecomposesaidgas; I

8:; The; method: making; a; lightesensi-tive. cathodezwhich 2 comprises depositing .a--' layer of SHVYDIIL34IIOH1OHYQI the; inside:- surfaoe: of an evacuated glass tube; oxidizing the surface of-said: silver layer, exposing said oxidized silver layer to antimony hydride gas, heating said layer to decompose said gas, and exposing said layer of antimony to cesium vapor to form a layer of cesium thereon.

9. The method of forming a metallic layer as a component part of a, light-sensitive electrode which comprises evacuating a container, intro-.

ducing into said container a gaseous hydride of a metal of the fourth and fifth groups of the periodic table, and decomposing said hydride to form a deposit of the metal of said hydride on an electrode carrier inside said container.

10. The method of forming a metallic layer which comprises evacuating a container, introducing into said container a gaseous hydride of a metalof the fourth and fifth groups of the periodic table, decomposing said hydride to form a deposit of the metal of said hydride on an electrode carrier inside said container, and introtainer.

12. The method of forming a metallic layer which comprises evacuating a container, introducing into said container a gaseous hydride of a metal of the fourth and fifth groups of the periodic table, and heating an electrode carrier inside said container to decompose said hydride to form a deposit'of the metal of said hydride on said electrode carrier.

13. The method of forming a metallic layer which comprises evacuating a container, introducing into said container a gaseous hydride of a metal of the fourth and fifth groups of the periodic table, heating an electrode carrier inside said container to decompose said hydride to form a deposit of the metal of said hydride on I of said silver oxide, introducing antimony hydride said electrode carrier, and introducing an alkali metal into said container in the form or; de-

posit on said deposit of metal: t 7 v 14. The method of forming a metallic. layer which comprises evacuating a container, introducing into said container a gaseous hydride i? a metal. of the fourth and fifth groups of the periodic table, producing'an electric discharge within said container-to decompose said hydride comprises forming intimate layers of an alkali I metal and another element within an evacuated container, the layer of said other element being formed by introducing into said container a gaseous hydride of an element of the fourth and fifth groups of the periodic table and decomposing said hydride to form the said layer of said element;

16. The method of making a'light sensitive cathode which comprises forming a light sensi- [hydride to.1'orm a deposit of antimony on said layer; 1

1'7. The method. of making a light-sensitive cathode which comprises forming alayer of silveron the inside wall of a vacuum container,

oxidizing the surface of said silver, forming a composite layer comprising antimony and caesium in intimate contact with each other on said oxidized surface by introducing antimony hydride gas in said container and decomposing the gas byheating the wall on which the silver is deposited to 150 to 200 C. and by depositing the caesium from caesium vapor, said steps of depositing antimony and caesium being per- -5' formed one after the other.

18. The method of making a light-sensitive cathode which comprises depositing caesium on oxidized silver, heat treating said caesium, silver and silver oxide to form a matrix which is sensitive to light, and further heating said matrix in the presence of a gaseous hydride of a metal of the fourth and fifth groups of the periodic table to a temperature sufflcient to decompose said hydride to form a deposit of said metal on said tive layer of cesium, and'heating said layer in matrix.

the presence of antimony hydride gas to a temperature sufficient to decompose said antimony GORDON K. TEAL. 

